Release 10 of the 3rd Generation Partnership Project Evolved Universal Terrestrial Radio Access (E-UTRA) specifications introduces Carrier Aggregation (CA). In CA, two or more component carriers (CCs) are aggregated in order to support wider transmission bandwidths up to 100 MHz. A User Equipment capable of CA may simultaneously receive or transmit on one or multiple CCs depending on its capabilities.
In CA, the UE can be configured to aggregate a different number of CCs originating from the same evolved NodeB (eNB) and of possibly different bandwidths in the uplink (UL) and downlink (DL). The UE can be configured with a primary cell (PCell) that is used for security, Non Access Stratum (NAS) mobility and transmission of Physical Uplink Control Channel (PUCCH). Other configured CCs are called secondary cells (SCells) and do not have PUCCH configured.
The CA supports a possibility to de-activate CCs/SCells in order to reduce the UE power consumption. The UE monitoring activity of a de-activated SCell is reduced (e.g. no Physical Downlink Control Channel (PDCCH) monitoring nor Channel Quality Indicator (CQI) measurements are performed) and the Uplink (UL) activity, for example transmission of Sounding Reference Signals (SRSs), in a de-activated carrier is also stopped. However, the PCell, which carries PUCCH cannot be deactivated.